3 Lots of little impacts
You might think that craters on the Moon are all pretty old, but you’d be wrong. The craters that are big enough to see through a telescope are old, but the Moon is being hit by cosmic debris all the time. With no atmosphere to protect it, even small chunks of rock and ice strike the surface with undiminished speed. When that happens, there is a brief flash of light as the energy of the impact gets turned into heat.
This image shows the locations of hundreds of meteoroid impacts detected since 2005 by a NASA-led campaign using telescope cameras. One of the brightest flashes and therefore one of biggest impacts was on 17 March 2013 (the red square above), as you will see next.
If you wanted to look into this further, you might find the following link of interest:222 new craters (10 m to 43 m in size) found by comparing high-resolution images from NASA’s Lunar Reconnaissance Orbiter. Short article and animation.